arXiv 1503.065392015-03gr-qcastro-ph.COhep-phhep-th

Horndeski以外理论的观测特征

Observational signatures of the theories beyond Horndeski

Antonio De Felice, Kazuya Koyama, Shinji Tsujikawa

备注：: 20 pages, 4 figures, published in JCAP
发表信息：: JCAP 1505 (2015) 058
DOI：: 10.1088/1475-7516/2015/05/058

摘要：

在修正引力的有效场论方法中，我们导出了在平坦各向同性宇宙学背景下，正压理想流体存在时的线性扰动运动方程。在一个简单版本的Gleyzes-Langlois-Piazza-Vernizzi（GLPV）理论，这是Horndeski理论的最小扩展，我们表明，张量传播速度的平方$c_{\rm t}^2$从1的轻微偏差通常会导致大的修改的传播速度的平方$c_{\rm s}^2$的标量自由度$ϕ$。只要场$ϕ$的动能$ρ_X$比背景能量密度$ρ_m$小得多，这个问题就一直存在，这是过去渐近的大多数暗能量模型的情况。由于以常数比$ρ_X/ρ_m$为特征的标度解是避免这一问题的一种方法，我们在Jordan框架下的GLPV理论框架下研究了标度暗能量模型的微扰演化.如果标量扰动的振荡模式被微调，使得它最初被抑制，则两个引力势$Ψ$和$Φ$之间的各向异性参数$η=-Φ/Ψ$对于远离1的$c_{\rm t}^2$显著偏离1。对于其它一般的初始条件，当$c_{\rm t}^2$偏离1时，$Ψ$将出现频率与$c_{\rm s}^2$有关的大振荡.在这两种情况下，该模型可以留下明显的印记的观测CMB和弱透镜。

英文摘要：

In the approach of the effective field theory of modified gravity, we derive the equations of motion for linear perturbations in the presence of a barotropic perfect fluid on the flat isotropic cosmological background. In a simple version of Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories, which is the minimum extension of Horndeski theories, we show that a slight deviation of the tensor propagation speed squared $c_{\rm t}^2$ from 1 generally leads to the large modification to the propagation speed squared $c_{\rm s}^2$ of a scalar degree of freedom $ϕ$. This problem persists whenever the kinetic energy $ρ_X$ of the field $ϕ$ is much smaller than the background energy density $ρ_m$, which is the case for most of dark energy models in the asymptotic past. Since the scaling solution characterized by the constant ratio $ρ_X/ρ_m$ is one way out for avoiding such a problem, we study the evolution of perturbations for a scaling dark energy model in the framework of GLPV theories in the Jordan frame. Provided the oscillating mode of scalar perturbations is fine-tuned so that it is initially suppressed, the anisotropic parameter $η=-Φ/Ψ$ between the two gravitational potentials $Ψ$ and $Φ$ significantly deviates from 1 for $c_{\rm t}^2$ away from 1. For other general initial conditions, the deviation of $c_{\rm t}^2$ from 1 gives rise to the large oscillation of $Ψ$ with the frequency related to $c_{\rm s}^2$. In both cases, the model can leave distinct imprints for the observations of CMB and weak lensing.

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英文摘要：

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